The present disclosure relates to an image forming apparatus.
In an electrophotographic color image forming apparatus, a color image is formed by superimposing and transferring images of respective colors on a recording medium placed on a conveying belt or an intermediate transfer belt.
If the image forming position (registration) of each color with respect to the recording medium or the intermediate transfer belt is misaligned and the images of the colors hence cannot be correctly superimposed and transferred, a good color image cannot be formed.
For example, in a direct tandem type image forming apparatus, a sensor is disposed at a position which is opposed to a recording medium conveying surface of the conveying belt. A registration correction image is formed on the conveying belt, and the sensor reads the registration correction image to detect misalignment of the registration. Then, the timing of exposure on the surface of a photosensitive member by an exposing device is adjusted, thereby preventing misalignment of the registration from occurring.
Further, in order to prevent the density of a toner image from being changed due to the aging of the apparatus, a change in the environment, or the like, a density correction image is formed on the conveying belt, and the density of the density correction image is detected by a sensor, thereby controlling the image density.
The above-described correction images are removed from the conveying belt by a cleaning unit which is opposed to the recording medium conveying surface of the conveying belt.
As such a cleaning unit, a unit having a cleaning roller which is placed so as to butt against a conveying belt is known. In a portion where the cleaning roller butts against the conveying belt, the cleaning roller rotates in the direction opposite to the moving direction of the conveying belt, and removes a correction pattern on the conveying belt.